Electrospinning Equipment for Research| Designing Flexible Carbon Nanofiber Membranes by Electrospinning and CrossLinking for Proton Exchange Membrane Fuel Cells

 Research Team Led by Prof. Li Yuping at Institute of Process Engineering, Chinese Academy of Sciences: High-Performance Flexible Carbon Nanofiber Membranes for Proton Exchange Membrane Fuel Cells

With the global energy demand surging and environmental issues caused by fossil fuels becoming increasingly severe, the development of clean energy technologies is urgent. Proton exchange membrane fuel cells (PEMFCs) have shown great potential in transportation, portable devices, and distributed power generation due to their zero emissions, high efficiency, and sustainability. The gas diffusion layer (GDL) is one of the core components of PEMFCs, requiring high mechanical strength and conductivity, appropriate porosity, and hydrophilicity/hydrophobicity (to prevent flooding and facilitate water removal). However, conventional carbon-based GDLs struggle to meet all these requirements simultaneously, limiting PEMFC commercialization.

Recently, the research team led by Prof. Li Yuping and Prof. Cao Hongbin at the Institute of Process Engineering, Chinese Academy of Sciences, prepared carbon nanofiber membranes (CFMs) with high flexibility, mechanical strength, conductivity, and electrochemical performance through electrospinning and impregnation crosslinking processes (fabrication process shown in Figure 1). The findings were published in ACS Applied Materials & Interfaces under the title "Designing Flexible Carbon Nanofiber Membranes by Electrospinning and Crosslinking for Proton Exchange Membrane Fuel Cells."

Figure 1: Fabrication process flowchart

Polyacrylonitrile (PAN)-based CFMs were prepared via electrospinning. SEM images showed that CFMs without carbon nanotubes (CNTs) had smooth surfaces with an average diameter of about 0.20 μm. After incorporating 1.5 wt% multi-walled carbon nanotubes (MWCNTs), fiber surface roughness increased, and the average diameter grew to 0.73 μm, forming an ordered three-dimensional porous network. After polyethyleneimine (PEI) impregnation and glutaraldehyde (GA) crosslinking, fiber bonding strengthened, porosity slightly decreased to 75.4%, but excellent gas transport capability was maintained (Figure 2).

Figure 2: SEM characterization: (a-h) Various CFM samples at different magnifications

XPS and FTIR analyses confirmed that PEI/GA crosslinking formed Schiff base structures, increasing nitrogen content from 3.38% to 6.94%, significantly enhancing membrane chemical stability (Figure 3).

Figure 3: FTIR and XPS analyses confirming successful PEI/GA crosslinking

Mechanical tests showed that CNT1.5/PEI7/GA-CFM exhibited superior tensile strength (7.94 MPa) and flexural strength (20.65 MPa) compared to untreated samples, along with good bending flexibility (Figure 4).Accelerated acid degradation tests demonstrated CFM structural stability, with the contact angle only slightly decreasing from 136° to 127°. The PTFE hydrophobic layer showed minor degradation, but fiber morphology remained intact without collapse, indicating excellent durability. These properties enable high performance even under harsh conditions.

Figure 4: Mechanical properties of CNT-doped CFM and PEI/GA-treated CFM

CFM in-plane resistivity initially increased then decreased with MWCNT content, reaching the lowest value (50.10 mΩ·cm) at 1.5 wt%. PEI impregnation and GA crosslinking further reduced resistivity to 18.60 mΩ·cm, attributed to MWCNT conductive networks and active sites provided by PEI/GA. Single-cell tests showed that CNT1.5/PEI7/GA-CFM achieved a peak power density of 1169 mW·cm-2 at 80°C and 100% relative humidity, outperforming commercial GDLs and demonstrating excellent electrochemical performance (Figure 5).

Figure 5: Electrochemical performance of CNT-doped CFM and PEI/GA-treated CFM

Electrochemical impedance spectroscopy (EIS) results indicated lower impedance for CNT1.5/PEI7/GA-CFM, suggesting better proton and electron transport. Further EIS tests at high current densities revealed that data could not be fitted using equivalent circuits. Instead, distribution of relaxation times (DRT) analysis qualitatively assessed relaxation time and frequency-dependent impedance changes, showing that PEI/GA-crosslinked samples had fewer relaxation processes and shorter relaxation times, effectively reducing impedance and accelerating proton/electron transport response, consistent with impedance spectrum conclusions (Figure 6).

Figure 6: EIS and DRT analysis of PEI/GA-treated CFM

Compared to commercial GDLs, CNT1.5/PEI7/GA-CFM exhibited superior porosity (75.4%), average pore size (1664 nm), and total pore volume (2.76 mL/g), balancing gas transport and structural integrity. Its mechanical properties—tensile strength (7.94 MPa), flexural strength (20.65 MPa), and bending modulus (3027 MPa)—were also outstanding, enhancing durability and lifespan for practical applications. Both limiting current density and power density surpassed commercial GDLs, demonstrating great potential as next-generation GDLs for transportation, portable devices, and distributed power generation.

By combining electrospinning with crosslinking technology, this study provides an innovative solution for PEMFC scale-up applications with broad commercialization prospects.

Paper link: https://pubs.acs.org/doi/full/10.1021/acsami.5c02589